1. Field of the Invention
This invention relates to spring powered switches, and to testing of the mechanical operation of spring powered switches such as medium voltage circuit breakers.
2. Background Information
Switches carrying sizable electric currents, such as medium voltage circuit breakers, require substantial mechanical forces to operate the switch rapidly and to hold the contacts closed against the magnetic repulsion forces generated by the current. In a typical medium voltage circuit breaker, a set of charged closing springs is released to close the breaker and to charge an opening spring which, in turn, is later released to open the breaker. The speed at which the mechanism operates is so rapid that it is difficult to identify the nature of any malfunctions, or even in some cases, to discern that the breaker is not operating properly.
Under typical practice, a skilled engineer is dispatched to the field or the circuit breaker must be returned to the factory to determine the cause and remedy for a malfunction or impaired performance. Due to the high inertia developed in the operating mechanism, there is considerable overshoot and distortion of the parts during operation. Often, analysis, which typically is performed using an expensive camera system, is qualitative rather than quantitative (e.g., it is determined that there is excessive overshoot, but no measurement of the amount of overshoot is provided). This technique for analyzing the operation of such switches is expensive and time consuming, and is highly dependent upon the skill and experience of the tester.
U.S. Pat. No. 5,726,367 discloses a method and apparatus for testing the operation of a spring powered switch mounted in a support frame and operated by an operating mechanism having driven parts actuated by release of charged springs. A recording medium, such as a tape, is applied to one of the driven parts. A fixture mounted to the support frame adjacent the selected driven part supports a marking instrument in contact with the recording medium at a fixed point relative to the support frame. When the charged spring is released, the selected driven part, which carries the recording medium, moves relative to the marking instrument. This produces a trace on the recording medium representing the movement of the selected driven part relative to the fixed point. This trace provides a quantitative record of the movement of the selected driven part which can be used to analyze the performance of the operating mechanism of the switch.
N. Anger et al., xe2x80x9cDiagnostics/Monitoring for Medium-Voltage Components and Systemsxe2x80x9d, pp. 1.14.1-1.14.4, discloses the detection of the angle of rotation curve for the breaker shaft of a vacuum circuit breaker""s spring-stored-energy operating mechanism. An expert circuit breaker diagnostic system employs temperature sensors, current transformers, and an angle resolver to provide temperatures, opening and closing solenoid coil currents and charging motor currents, and shaft angles to a microprocessor in a continuous on-line operation. Trend analyses are performed using parameters of individual past switching operations with the aid of temperature, voltage and time-compensated classification models.
Although it is known to employ mechanical or electronic sensors for sensing movement of certain operating mechanism components to test a circuit breaker, there remains a need, however, for an improved method and apparatus for ready and inexpensive testing of spring operated switches.
This need and others are satisfied by the invention which is directed to a spring powered switch. The switch is operated by an operating mechanism including a driven part having a variable angular position. A rotary potentiometer tracks the variable angular movement of the driven part. The output signal of the potentiometer corresponds to the driven part""s variable angular movement. The output signal is monitored with respect to time in order to monitor the angular movement of the driven part with respect to time.
As one aspect of the invention, a method of testing a spring powered switch comprises the steps of selecting one of a plurality of driven parts actuated by release of a charged spring; releasing the charged spring to actuate the driven parts and produce angular movement of the selected one of the driven parts; energizing a rotary potentiometer; tracking angular movement of the selected one of the driven parts with the rotary potentiometer to produce a variable output signal therefrom which corresponds to the angular movement; and monitoring the output signal with respect to time in order to monitor the angular movement of the selected one of the driven parts with respect to time.
As a preferred refinement, an eccentric surface is employed on the selected one of the driven parts; the eccentric surface is followed with a wheel; the wheel is employed to monitor angular movement of the selected one of the driven parts; and the potentiometer is adjusted with the wheel.
As another aspect of the invention, an apparatus for testing a spring powered switch including a driven part having a variable angular position comprises a potentiometer having an input and a rotary shaft; means for energizing the input of the potentiometer; means for engaging the driven part to adjust the rotary shaft of the potentiometer and produce a variable output signal therefrom which corresponds to variable angular movement of the driven part; and means for monitoring the output signal with respect to time in order to monitor the angular movement of the driven part with respect to time.
As a preferred refinement, the spring powered switch includes a support member adjacent the driven part, the driven part has an eccentric surface, and the means for engaging the driven part includes: a wheel being in rotational contact with the eccentric surface of the driven part; and means for rotatably supporting the wheel with respect to the support member and for following the eccentric surface with the wheel. An axle of the wheel rotates in response to the variable angular position of the driven part.
As a further aspect of the invention, a spring powered switch comprises separable contacts having an open position and a closed position; means for operating the separable contacts between the open and closed positions; and a test assembly. The means for operating includes a driven part having a plurality of angular positions and a closing spring for actuating the means for operating to move the driven part between the angular positions. The test assembly comprises a potentiometer having an input and a rotary shaft; a voltage source connected to the input of the potentiometer; means for engaging the driven part having a linkage which rotates in response to the variable angular position of the driven part; and means for monitoring the output voltage with respect to time in order to monitor the angular movement of the driven part with respect to time. The linkage engages the rotary shaft of the potentiometer to adjust the potentiometer and produce a variable output voltage. The output voltage corresponds to the angular movement of the driven part.